The success of rotary drilling enabled the discovery of deep oil and gas reservoirs and production of enormous quantities of oil. The rotary rock bit was an important invention that made the success of rotary drilling possible. Only soft earthen formations could be penetrated commercially with the earlier drag bit and cable tool, but the two-cone rock bit, invented by Howard R. Hughes, U.S. Pat. No. 930,759, drilled the caprock at the Spindletop field near Beaumont, Tex., with relative ease. That venerable invention, within the first decade of the last century, could drill a scant fraction of the depth and speed of the modern rotary rock bit. The original Hughes bit drilled for hours; the modern bit now drills for days. Modern bits sometimes drill for thousands of feet instead of merely a few feet. Many advances have contributed to the impressive improvements in rotary rock bits.
In drilling wellbores in earthen formations using rolling-cone bits, which may also be characterized as “rock bits,” such bits having one or more rolling cones rotatably mounted thereon are employed. The term “cone” is a term of art, as other shapes of rolling structures used in drilling subterranean formations are conventional. The bit is secured to the lower end of a drill string that is rotated from the surface or by downhole motors or turbines. The cones are rotationally mounted on legs of the bit roll and slide upon the bottom of the wellbore as the drill string is rotated, to engage and disintegrate the formation material to be removed. The rolling cones are provided with cutting elements or teeth, which may be integral with the cones or inserts secured to the cones, that are forced to penetrate and gouge the bottom of the wellbore by weight from the drill string. Other, so-called “hybrid,” drill bits employ rolling cones in combination with fixed cutters mounted on blades extending from the drill bit body. The formation cuttings from the bottom and sides (i.e., the wall) of the wellbore are washed away and disposed by drilling fluid that is pumped down from the surface through the hollow, rotating drill string, and the nozzles as orifices on the drill bit. Eventually the cuttings are carried in suspension in the drilling fluid to the surface up the exterior of the drill string in the wellbore annulus.